Re: [M3UA] ASP UP in IPSP DE mode

Brian and Santhana,

Noting first that "Brian was there", and "I was not",
I had considered that the DE mode was to cater to
different ASP states at each end of the IPSP pairing.

I think this means that in DE mode, sending an ASP-UP-Ack
meant that you were permitting the other side to enter
ASP UP state, but weren't implying that you were requesting
the same for your own state.

The usefulness of one side being UP and the other side
not UP in a single peer-to-peer relationship is beyond
my imaginings, though.  I think Brian's implication
is that if you are allowing the other side to move to
ASP-UP then you are admitting that you are happy to go
ASP-UP too, and I agree that SE is always the preferred
IPSP mode.

With thanks, from Chris Benson.

On Thu, 6 Jan 2011, Brian F. G. Bidulock wrote:

>>  Date: Thu, 6 Jan 2011 02:45:50 -0700
>>  From: Brian F. G. Bidulock <[email protected]>
>>  To: Santhana <[email protected]>
>>  Cc:  <[email protected]>
>>  Subject: Re: [Sigtran] [M3UA] ASP UP in IPSP DE mode
>>  
>>  Santhana,
>>  
>>  Please see comments below...
>>  
>>  Santhana wrote:                               (Thu, 06 Jan 2011 10:26:34)
>>  >    Dear Brian
>>  > 
>>  >                In IPSP DE mode, is the double exchange of ASP UP messages
>>  >    mandatory? As per the M3UA RFC 4666, in section 4.3.4.1.2 para2 says
>>  >    double exchange of ASPSM is MUST.
>>  > 
>>  >    Whereas in section 5.6.2 in the sequence diagrams it says second
>>  >    exchange is optional.
>>  > 
>>  > 
>>  >    If it is mandated, then what purpose it solves?
>>  > 
>>  > 
>>  >    Regards
>>  > 
>>  >    Santhanakrishnan
>>  
>>  I don't know what purpose it solves.  There was a change from RFC3332 to
>>  RFC4666 in 4.3.4.1.2 para2, but the example in 5.6.2 did not change.  But
>>  then the editor of RFC4666 did a poor job of keeping examples up to date
>>  with the text.
>>  
>>   RFC 4666
>>  
>>     Alternatively, when using the IPSP DE model, an interchange of ASP Up
>>     messages from each end MUST be performed.  Four messages are needed
>>     for completion.
>>  
>>   RFC 3332
>>  
>>     Alternatively, an interchange of ASP Up messages from each end can be
>>     performed. This option follows the ASP state transition diagram. It
>>     would need four messages for completion.
>>  
>>  The only reason I can remember for requiring double exchange of ASP-UP
>>  for DE was so that a misconfiguration between SE and DE would be detected.
>>  The original intent from RFC 3332 is described at the end of example
>>  RFC4666/5.6.2 or RFC3332/5.5.2 (which are identical).
>>  
>>     In this approach, only one single exchange of ASP Up message can be
>>     considered as enough since the response by the other peer can be
>>     considered as a notice that it is in ASP_UP state.
>>  
>>  But, in general, DE mode is always a situation of performing two message
>>  exchanges where one will do.  Use SE mode wherever possible.
>>  
>>  --brian
>>  
>>  -- 
>>  Brian F. G. Bidulock
>>  [email protected]
>>  http://www.openss7.org/
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